Permanent Concrete Formwork And Method For Manufacturing A Metal-Concrete Composite Structure Using Such A Formwork

ABSTRACT

The invention relates to a permanent concrete formwork for manufacturing a metal-concrete composite structure, comprising: two walls each comprising at least one metal plate, the walls being parallel, arranged opposite one another, and spaced apart from one another so as to define an inner space of the formwork; struts which connect the two walls and which attach the two walls to one another, the struts passing through the two walls and projecting from either side of the formwork; bars located on each of the walls and which project into the inner space of the formwork, wherein each metal plate is attached to the opposite metal plate by at least three struts, the first strut being located at a first end of the metal plate, the second strut being located at a second end opposite said first end, and the third strut being located in a central region located between the first end and the second end, and in that the struts comprise threaded ends, the struts being attached to the metal plate by bolting.

FIELD OF THE INVENTION

The present invention relates to a device forming a permanent metal formwork for the casting of concrete, and to the method for manufacturing a metal-concrete composite structure in which such a formwork is used.

More particularly, the invention relates to a permanent metal formwork and a manufacturing method making it possible to manufacture a metal-concrete composite structure with high mechanical strengths, for example for a nuclear power plant. However, the formwork and the method can be used for other constructions, such as for the construction of buildings, industrial buildings, or bridges.

STATE OF THE ART

In order to manufacture a concrete structure, it is known to use a formwork delimiting a volume in which concrete is cast. When the concrete is dry, the formwork is removed and a concrete structure, such as a wall, is thus obtained.

In general, in order to manufacture a concrete structure having a high mechanical strength, said structure is made of reinforced concrete.

Indeed, concrete is known for its compressive strength, but has a low tensile strength. A typical example of weakness of concrete is the case of a concrete floor of a storey that is maintained only at its contour, the central part of said floor being then very likely to collapse under its own weight due to the fact that its lower part is tense and that the tensile forces are not taken up.

To make a reinforced concrete structure, a metal reinforcement, generally formed of steel rods, is disposed in the volume delimited by the formwork, then the concrete is cast around said reinforcement, and once the concrete has hardened, the formwork is removed, thereby forming a concrete structure containing a metal reinforcement. The metal rods forming the metal reinforcement are placed in the tense areas of the structure in order to balance the internal forces and thereby ensure the stability of said structure.

In order to obtain a structure with very high mechanical strength, it is known to increase the density of the metal rods of the metal reinforcement. For example, in the reinforced concrete structures of the nuclear power plants, the density of steel in the reinforced concrete is approximately 4 times higher than in the standard reinforced concrete structures.

However, this technique for increasing resistance while increasing the reinforcement density is limited. Indeed, from a certain reinforcement density, it is no longer possible to properly place the reinforcements in the concrete because they interfere with each other.

Moreover, other problems arise, such as bad passage of aggregates between the rods of the reinforcement or the difficulty of getting rid of the air bubbles after casting of the concrete.

In addition, within the context of the construction of a nuclear power plant, the equipment or mechanical parts must be secured to an anchor platen in order to secure them to the reinforced concrete structure to be made.

In order to secure this platen to the structure to be manufactured, the platen has anchor shafts that are disposed so as to pass through the metal reinforcement. However, because of the high density of the metal reinforcement, passing the anchor shafts of the platen through the meshes of the iron framework formed by the metal rods composing the metal reinforcement becomes complicated, and it is sometimes necessary to twist the anchor shafts for passing said anchor shafts through the metal reinforcement. It may also be necessary to move the initial position of the platen to be able to pass the anchor shafts through the metal reinforcement.

Thus, the implementation of a platen is a very difficult task, and is not uncommon to have to make resumptions after removal of the formwork. Moreover, placing the platens lengthens very consistently the duration of the work.

Documents US 2003/0029111, EP2617910 and US 2010/0132291 are known. Documents JP S6047140, U.S. Pat. No. 4,211,045 and JP 2012 087538 are also known.

These documents describe an alternative solution to the reinforced concrete, for making concrete structures, which is the use of a permanent metal formwork which is an integral part of the concrete structure since it is not removed once the concrete has hardened. The permanent metal formwork allows providing the concrete with the tensile strength and thus fulfills the same function as the internal metal reinforcement of the reinforced concrete.

In order to connect the metal walls together, the permanent formwork comprises struts connecting said walls. The struts also allow ensuring cohesion between the concrete and the permanent formwork.

However, the use of a permanent formwork has several drawbacks. A first drawback is that it is necessary to ensure a good cohesion between the formwork and the concrete cast thereinside in order to ensure that the structure has the desired resistance to mechanical forces.

Another drawback is that the anchoring of the platen remains problematic because the platen must be secured on the formwork, which is done by welding, which welding causes problems of deformations of the platen or formwork.

An additional drawback is also the fact that the maximum load that the platen withstands depends on its position on the structure relative to the struts. Indeed, a platen secured on the permanent formwork directly facing a strut can withstand a much higher maximum load than a platen that is not directly secured facing a strut.

Thus, there is currently no solution for manufacturing a reinforced concrete structure that has great resistance to mechanical forces, without any problem for the implementation in relation to the density of the metal reinforcement, on which a platen whose resistance is certain can be easily secured.

GENERAL PRESENTATION OF THE INVENTION

An object of the invention is to propose a permanent metal formwork for concrete allowing to manufacture a metal-concrete composite structure that has great resistance to mechanical forces, on which a platen can be easily secured, and whose maximum load that the platen can withstand is certain and significant.

Another object of the invention is to propose a method for manufacturing a concrete structure with high resistance to mechanical forces, the method being simple to implement and allowing to easily secure a platen to the structure, the maximum load that said platen can withstand being certain and significant.

For this purpose, a permanent concrete formwork is provided for the manufacture of a metal/concrete composite structure, said formwork comprising:

-   -   two walls each formed of at least one metal plate, said walls         being parallel, located facing each other and spaced apart from         each other so as to delimit an internal volume of the formwork;     -   struts connecting the two walls and securing said two walls         together, the struts passing right through said two walls and         thereby protruding from each side of the formwork;     -   bars located on each of the walls and protruding in the internal         volume of the formwork;

characterized in that each metal plate is secured to the opposite metal plate by at least three struts, a first strut being located at a first end of the metal plate, a second strut being located at a second end opposite said first end, and a third strut being located in a central region located between said first end and said second end, and in that the struts comprise threaded ends, the struts being secured to the metal plate by bolting, and characterized in that the walls comprise two metal plates placed end-to-end, said formwork further comprising an assembly rod only deposited on the struts and/or on the bars, said assembly rod comprising a protrusion at each of its ends.

The fact of using a permanent formwork makes it possible to eliminate the need of internal metal reinforcements of the reinforced concrete to make a concrete structure.

In addition, the fact that the metal plate is connected to the metal plate located facing it by at least three struts distributed within the length of said metal plate allows, on the one hand, strengthening the resistance to mechanical forces that the formwork provides to the concrete structure and, on the other hand, ensuring a constant spacing between the walls of the formwork.

In addition, the fact that the struts are threaded rods projecting from the walls of the formwork and secured to the walls of the formwork by bolting allows, on the one hand, visualizing the position of struts and therefore easily calculating the maximum mechanical strength that a platen secured to the formwork can withstand and, on the other hand, easily securing additional elements on the formwork, such as for example platens for accessories of the second work.

The device according to the invention is advantageously completed by the following characteristics, taken alone or in any of their technically possible combinations:

-   -   the assembly rod is adapted to be placed inside the internal         volume of the formwork facing the connection between the two         metal plates,     -   the bars located at the periphery of the metal plates have a         diameter greater than the diameter of the bars located in the         center of said metal plates, and/or the number of bars per unit         area is greater at the periphery of the metal plates than in the         center of said metal plates, the assembly rod resting on the         bars at the periphery of the metal plates;     -   the formwork comprises a sealing plate disposed on the formwork         outside the internal volume and removably secured to struts, the         sealing plate being located at the ends of two metal plates         adjacent over an entire height of the two metal plates, so that         the sealing plate overlaps said two metal plates adjacent over         their entire height;     -   the formwork comprises an alignment beam disposed on the         formwork outside the internal volume and removably secured to         struts, said alignment beam being secured to two metal plates         adjacent over at least half a length of the metal plates.

The invention also relates to an assembly comprising two permanent concrete formworks according to any one of the above-mentioned characteristics, wherein said formworks are assembled so that the assembly is L-shaped and that the internal volumes of said formworks communicate with each other, the assembly further comprising connection rods for securing said formworks together, a first connection rod comprising a first end secured by bolting to a wall of a first formwork and a second end comprising a protrusion and located inside the internal volume of a second formwork, a second connection rod comprising a first end secured to a wall of the second formwork and a second end comprising a protrusion and located inside the internal volume of the first formwork.

The invention also relates to an assembly comprising two permanent concrete formworks according to any one of the above-mentioned characteristics, wherein said formworks are assembled so that the assembly is T-shaped and that the internal volumes of said formworks communicate with each other, a first formwork comprising a first wall that comprises two metal plates located facing a metal plate forming a second wall of said first formwork, a second formwork being located between the two metal plates of the first wall of said first formwork, said assembly further comprising connection rods for securing said formworks together, a first connection rod comprising a first end secured to the metal plate forming the second wall of said first formwork and a second end located inside the internal volume of the second formwork, a second connection rod comprising two ends that comprise each a protrusion and that are located in the internal volume of said first formwork.

The invention also relates to an assembly comprising four permanent concrete formworks according to any one of the above-mentioned characteristics, wherein said formworks are assembled so that the assembly is cross-shaped and that the internal volumes of said formworks communicate with each other, said assembly further comprising connection rods for securing said formworks together, a first connection rod comprising a first end that comprises a protrusion and that is located in the internal volume of a first formwork, and a second end that comprises a protrusion and that is located in the internal volume of a second formwork, a second connection rod comprising a first end that comprises a protrusion and that is located in the internal volume of a third formwork, and a second end that comprises a protrusion and that is located in the internal volume of a fourth formwork.

The invention also relates to a method for manufacturing a concrete structure characterized in that it comprises the following steps:

-   -   providing a permanent concrete formwork according to any one of         the previously defined characteristics;     -   casting concrete inside the internal volume of the formwork.

The method may comprise the following step:

-   -   securing a platen to at least one strut of the formwork by         bolting.

The invention also relates to a metal/concrete composite structure obtained according to the manufacturing method according to any one of the above-mentioned characteristics.

According to another aspect making it possible to easily assemble without welding the metal plates forming the walls of the formwork, the invention relates to a permanent concrete formwork for the manufacture of a metal/concrete composite structure, said formwork comprising:

-   -   two walls each formed of at least two metal plates placed         end-to-end, said walls being parallel, located facing each other         and spaced apart from each other so as to delimit an internal         volume of the formwork;     -   struts connecting the two walls and securing said two walls         together;     -   bars located on each of the walls and protruding in the internal         volume of the formwork;     -   an assembly rod only disposed on the struts and/or on the bars         facing a connection between two metal plates of the same wall,         said assembly rod comprising a protrusion at each of its ends.

Such a formwork may comprise the optional characteristics mentioned above.

PRESENTATION OF THE FIGURES

Other characteristics, objects and advantages of the invention will become apparent upon reading the following description of different embodiments represented in the following drawings:

FIG. 1 represents a perspective view of a permanent concrete formwork according to one embodiment before concrete is cast thereinside;

FIG. 2 represents a sectional view of the formwork of the part 1 at a central part of a metal plate forming a wall of the formwork;

FIG. 3 represents a sectional view of the formwork of the part 1 at a peripheral part of metal plates forming a wall of the formwork and showing the connection rods making the assembly system making it possible to eliminate the need of the “butt” welding of the sheets;

FIG. 4 represents a possible variant of the formwork of FIG. 1;

FIG. 5 represents a concrete structure obtained by using the formwork of FIG. 1, said structure comprising first and second possible variants of platens secured to the formwork;

FIG. 6 represents a concrete structure obtained by using the formwork of FIG. 1, said structure comprising a third possible variant of platens secured to the formwork;

FIG. 7 represents a perspective view of an L-shaped assembly formed by two formworks assembled together, front concrete is cast thereinside;

FIG. 8 represents a sectional view of the assembly of FIG. 7;

FIG. 9 represents a perspective view of a T-shaped assembly formed by two formworks assembled together, before concrete is cast thereinside;

FIG. 10 represents a more detailed vision of the assembly of FIG. 9 at the connection area between the formworks;

FIG. 11 represents a sectional view of the assembly of FIGS. 9 and 10;

FIG. 12 represents a perspective view of a cross-shaped assembly formed of four formworks assembled together, before concrete is cast thereinside;

FIG. 13 represents a sectional view of the assembly of FIG. 12;

FIG. 14 represents in a schematic form a possible implementation of the method for manufacturing a concrete structure according to the invention.

DESCRIPTION OF THE INVENTION

As represented in FIGS. 1, 2 and 3, a permanent concrete formwork 10 for the manufacture of a metal/concrete composite structure comprises two walls 20 and 30 that are located facing each other and that are parallel to each other. The two walls 20 and 30 are spaced apart so that the formwork 10 comprises an internal volume 40 delimited by said two walls 20 and 30.

The two walls 20 and 30 each comprise at least one metal plate 50. In the example illustrated in FIGS. 1 to 3, the walls 20 and 30 each comprise two metal plates 50 disposed one after the other in the same plane. The metal plates 50 may for example be made of steel.

In order to secure the walls 20 and 30 together, the formwork 10 comprises struts 60. The struts 60 pass right through said two walls 20 and 30 by protruding from each side of the formwork 10. The struts 60 are intended to be taken in the concrete once the concrete is cast inside the volume 40 of the formwork 10.

A plurality of struts 60 is distributed over the entire surface of the walls 20 and 30 of the formwork 10, preferably in a regular manner. The struts 60 make it possible to ensure the resistance to mechanical forces of the formwork 10. The struts 60 also make it possible to ensure that the spacing between the walls 20 and 30 is constant.

In order to provide the formwork 10 with a good resistance to mechanical forces, each metal plate 50 is secured to the metal plate 50 located facing it by at least 3 struts 60. A first strut 60 is located at a first end of the metal plate 50, a second strut 60 is located at a second end of said metal plate 50 opposite the first end, and a third strut 60 is located in a central area of said metal plate 50.

The struts 60 are formed of a threaded rod at its two ends which are secured to the walls 20 and 30 by bolting. The fact that the struts are rods, at least the ends of which are threaded and secured by bolting to the walls 20 and 30, makes it possible to easily secure elements to the formwork 10 by screwing them to the threaded ends of the struts 60 which protrude from the formwork 10.

As can be seen in FIGS. 2 and 3, the bolts that secure the struts 60 to the walls 20 and 30 of the formwork 10 may be formed by two nuts. A first nut 61 which is located inside the internal volume 40, and a second nut 62 which is located outside the internal volume 40 of the formwork 10.

In addition, the fact that the struts 60 protrude from the formwork 10 makes it possible to know where the struts 60 are located in the metal/concrete structure once the concrete is cast inside the formwork 10 (as can be seen in FIGS. 5 and 6), thereby making it possible to easily estimate the resistance to mechanical loads that the equipment can withstand when it secured to the metal/concrete structure.

The formwork also comprises bars 70 on each of the walls 20 and 30 and which protrude in the internal volume 40 of the formwork 10. The bars 70 are also called “studs” in the technical field of the manufacture of metal/concrete composite structure. The bars 70 comprise a first end which is secured to the walls 20 or 30, for example by welding, and a second end directed towards the inside of the internal volume 40 of the formwork 10. The bars 70 have the function of ensuring good cohesion between the walls 20 and 30 and the concrete which is cast into the internal volume 40. Once the concrete is cast inside the hardened formwork 10, the bars 70 take up the shearing forces between the walls 20 and 30 and the concrete. The bars 70 preferably comprise a protrusion at their second end.

As can be seen in FIG. 3, the formwork 10 comprises an assembly rod 80 located inside the internal volume 40 facing the connection between two metal plates 50 forming the walls 20 and 30. In the embodiment illustrated in FIG. 3, the formwork 10 comprises a plurality of assembly rods 80. The assembly rod 80 is located at the connection between two metal plates 50 forming the same wall 20 or 30, so as to be facing the two metal plates 50 forming said same wall 20 or 30. Thus, a first part of the assembly rod 80 is located facing a peripheral area of a first metal plate 50 forming a wall 20 or 30, and a second part of said assembly rod 80 is located facing a peripheral area of a second metal plate 50 forming said same wall 30.

The assembly rod 80 comprises a first end 81 and a second end 82 which both comprise a protrusion. The protrusions at the ends 81 and 82 of the assembly rod 80 may be formed by nuts screwed to the ends 81 and 82 of said assembly rod 80. The assembly rod 80 has the function of holding in position the metal plates 50 forming the same wall 20 or 30. Indeed, when the concrete is cast inside the internal volume 40 and has hardened, the presence of the assembly rod 80 makes it possible to create a mechanical connection of the metal plates 50 forming the same wall 20 or 30.

The assembly rod 80 is preferably only deposited on the bars 70 and/or on the struts 60 so that its installation in the formwork 10 is particularly easy. The assembly rod 80 is therefore not secured to the struts 60 and to the bars 70. However, according to one possible variant, the assembly rod 80 can be secured by a plastic insert to the bars 70, to the struts 60 or to the walls 20, 30. The assembly rod 80 may also be secured by a wire, for example an iron wire, to the bars 70, to the struts 60 or to the walls 20, 30 in order to hold it in position.

The assembly rod 80 makes it possible to assemble the metal plates 50 without welding. The fact of using the assembly rod 80 also makes it possible to reduce the positioning constraints of the metal plates 50, a slight offset being authorized with said assembly rod 80.

The bars 70 located at the periphery of the metal plate 50 have preferably a diameter greater than the diameter of the bars 70 located in the central part of said metal plate 50. Such a variant is advantageous because when the assembly rod 80 rests on the bars 70 located at the periphery of the metal plate 50, the mechanical forces taken up by the assembly rod 80 are transferred to the bars 70, thereby subjecting the bars 70 to flexional and shear stresses. According to one possible variant, the number per unit area of bars 70 located at the periphery of the metal plate 50 is greater than the number per unit area of bars located in the central part of said metal plate 50, so as to better take up the tensile forces of the assembly rod 80.

According to one possible variant illustrated in FIG. 4, the formwork 10 can comprise a sealing plate 90 which has the function of preventing concrete from being casted out of the internal volume 40 of the formwork 10 through the interstices that may exist between the metal plates 50 forming the same wall 20 or 30.

The sealing plate 90 is secured to the ends of the two adjacent metal plates 50 that form the same wall 20 or 30. The sealing plate 90 covers the end of the metal plates 50 over the entire height H of said metal plates 50.

The sealing plate 90 can be secured to the ends of the struts 60 that protrude out of the walls 20 and 30, for example by bolting. The sealing plate 90 may for example be a wooden plate. The sealing plate 90 is removable, it is removed once the concrete that has been cast inside the internal cavity 40 has hardened.

The formwork 10 may also comprise an alignment beam 91 that has the function of ensuring that the metal plates 50 forming the same walls 20 or 30 are indeed in the same plane. The formwork 10 advantageously comprises at least one alignment beam 91 on each of its walls 20 and 30.

The alignment beam 91 is secured on two adjacent metal plates 50 that form the same wall 20 or 30 outside the internal volume 40. The alignment beam 91 is removably secured, it is removed once the concrete that has been casted inside the internal cavity 40 has hardened. The alignment beam 91 is secured to the struts 60 that protrude out of the walls 20 and 30, for example by bolting.

The alignment beam 91 covers at least half a length L of each metal plate 50 on which said alignment beam 91 is secured. Such size of alignment beam 91 makes it possible to ensure better alignment of the two metal plates 50 adjacent in the same plane.

The variant illustrated in FIG. 4 comprises both sealing plates 90 and alignment beams 91, however, the formwork 10 may comprise only sealing plates 90, or comprise only alignment beams 91.

FIGS. 5 and 6 represent a metal/concrete composite structure 100 that has been manufactured with the permanent concrete formwork 10 according to the invention.

The metal/concrete structure 100 comprises a concrete layer B which is surrounded by the walls 20 and 30 of the formwork 10. The fact that the concrete layer B is surrounded by the formwork 10 allows the structure 100 to have a great resistance to mechanical forces without being in reinforced concrete.

FIGS. 5 and 6 illustrate a platen 110 a, 110 b, 110 c which is secured to said concrete structure 100. This platen 110 a, 110 b or 110 c allows securing elements of the second work to said concrete structure. As illustrated in these figures, the use of the formwork 10 allows easily securing the platens 110 a, 100 b, 110 c to the structure 100 by securing them by bolting to the ends of the struts 60 which protrude out of the concrete structure 100. Moreover, it is easy to estimate the maximum resistance of the platens 110 a, 110 b, 110 c, with the number of struts 60 to which said platens 110 a, 110 b, 110 c, are secured.

Such a formwork 10 allows a modular use of said formwork 10, so as to easily assemble formworks 10 in the desired manner to form a metal/concrete structure 100 of the desired shape.

FIGS. 7 and 8 represent one possible variant in which a first formwork 11 and a second formwork 12 are assembled to form an L-shaped assembly 200. For the assembly 200 to have an L shape, the formworks 11 and 12 are secured together by one of their end and are inclined together so as to form an angle. In the variant illustrated in FIGS. 7 and 8, the angle is of 90°. The first formwork 11 and the second formwork 12 comply with the embodiment described in FIGS. 1 to 4.

The formworks 11 and 12 are assembled so that the internal volumes 40 of said formworks 11 and 12 communicate with each other and therefore that the assembly 200 has a single internal volume. The concrete is cast inside this single internal volume of the assembly 200 to form the desired concrete structure.

The assembly 200 comprises connection rods 81 and 82 for securing the formworks 11 and 12 together. A first connection rod 81 comprises a first end which is secured to a wall of the first formwork 11, and a second end comprising a protrusion and which is located inside the internal volume 40 of the second formwork 12. A second connection rod 82 comprises a first end which is secured to a wall 20 of the second formwork 12, and a second end comprising a protrusion and which is located inside the internal volume 40 of the first formwork 11.

The protrusion located at the second end of the connection rods 81 and 82 may for example be formed of a nut which is screwed to said second end.

The first end of the connection rods 81 and 82 can be secured to the wall 20 of the formworks 11 and 12 by bolting. Such securing by bolting makes it possible to easily secure the connection rods 81 and 82 to the formworks 11 and 12.

Thus, preferably the connection rods 81 and 82 are rods similar to the assembly rods 80 described in FIGS. 1 to 4, said connection rods 81 and 82 being metal rods, generally steel rods, the two ends of which are threaded to be able to screw a nut therein.

The assembly 200 may comprise a plurality of first connection rods 81 and a plurality of second connection rods 82. The number of connection rods 81 and 82 is chosen in order to obtain the desired mechanical strength.

FIGS. 9, 10 and 11 illustrate one possible variant in which a first formwork 13 and a second formwork 14 are assembled to form a T-shaped assembly 210. The first formwork 13 and the second formwork 14 comply with the embodiment illustrated in FIGS. 1 to 4.

For the assembly 210 to have a T shape, the first formwork 13 and the second formwork 14 are inclined relative to each other, and the second formwork 14 is secured by one of its ends to a central region of the first formwork 13. The internal volumes 40 of the formworks 13 and 14 communicate with each other. In the variant illustrated in FIGS. 9, 10 and 11, the formworks 13 and 14 are inclined at an angle of 90°.

The first formwork 13 comprises a first wall 20 comprising two metal plates 50 that are located facing a metal plate 50 forming a second wall 30 of said first formwork 13. The second formwork 14 is secured between the two metal plates 50 of the first wall 20 of the first formwork 13.

The assembly 210 comprises connection rods 83 and 84 for securing the formworks 13 and 14 together. A first connection rod 83 comprises a first end secured to the second wall of the first formwork 13, and a second end comprising a protrusion and located in the internal volume 40 of the second formwork 14. A second connection rod 84 comprises a first end and a second end each comprising a protrusion, and which is located inside the internal volume 40 of the first formwork 13. The second connection rod 84 may be only deposited on the bars 70 and/or on the struts 60 of the first formwork 13.

The assembly 210 may comprise a plurality of first connection rods 83 and a plurality of second connection rods 84. The number of connection rods 83 and 84 is chosen to obtain the desired mechanical strength.

Preferably, the first connection rod 83 is secured to the second wall 30 of the first formwork 13 by bolting. The protrusions formed at the ends of the connection rods 83 and 84 may be formed by nuts screwed to said ends of said connection rods 83 and 84. The connection rods 83 and 84 may be similar to the connection rods 81 and 82 illustrated in FIGS. 7 and 8.

According to one possible variant, the T-shaped assembly 210 may also be formed of at least three formworks, this variant comprising two formworks instead of the first formwork 13.

FIGS. 9, 10 and 11 illustrate a possible variant in which a first formwork 15, a second formwork 16, a third formwork 17 and a fourth formwork 18 are assembled to form a cross-shaped assembly 220 (also called X shape). The formworks 15, 16, 17 and 18 comply with the embodiment illustrated in FIGS. 1 to 4. The internal volumes 40 of the formworks 15, 16, 17 and 18 communicate with each other.

For the assembly 220 to have a cross shape, the formworks 15, 16, 17 and 18 are all assembled by one end.

The assembly 210 comprises connection rods for securing the formworks 15, 16, 17 and 18 together.

A first connection rod 85 comprises a first end comprising a protrusion which is located in the internal volume 40 of the first formwork 15, and a second end comprising a protrusion which is located in the internal volume 40 of the second formwork 16.

A second connection rod 86 comprises a first end comprising a protrusion which is located in the internal volume 40 of the third formwork 17, and a second end comprising a protrusion which is located in the internal volume 40 of the fourth formwork 18.

The assembly 210 may comprise a plurality of first connection rods 85 and a plurality of second connection rods 86. The number of connection rods 85 and 86 is chosen in order to obtain the desired mechanical strength.

The protrusions formed at the ends of the connection rods 85 and 86 can be formed by nuts screwed to said ends of said connection rods 85 and 86. The connection rods 85 and 86 may be similar to the connection rods 81 and 82 illustrated in FIGS. 7 and 8.

As illustrated in FIG. 14, the method according to a possible implementation of the invention comprises the following steps:

-   -   1000: providing a permanent concrete formwork according to any         one of the variants of the invention. The concrete formwork may         be one of the variants described in the previous figures.     -   2000: casting concrete inside the internal volume of the         formwork. As a result of this step, and once the concrete has         hardened, a metal/concrete composite structure according to the         invention is obtained.     -   3000: securing a platen to at least one strut of the formwork by         bolting. This step is however optional, because a platen is         secured to the formwork only when an equipment is to be secured         to the concrete structure.

The method may also comprise a step in which formworks are assembled in order to form an assembly comprising several formworks, such as for example in the variants illustrated in FIGS. 9 to 13. The number of assembled formworks and the shape of the assembly are adapted according to the shape of the desired metal/concrete structure. The concrete is casted once the formworks are assembled. 

1. A permanent concrete formwork for the manufacture of a metal-concrete composite structure, said formwork comprising: two walls each formed of at least one metal plate, said walls being parallel, located facing each other and spaced apart from each other so as to delimit an internal volume of the formwork; struts connecting the two walls and securing said two walls together, the struts passing right through said two walls and thereby protruding from each side of the formwork; bars located on each of the walls and protruding in the internal volume of the formwork, wherein each metal plate is secured to the opposite metal plate by at least three struts, a first strut being located at a first end of the metal plate, a second strut being located at a second end opposite said first end, and a third strut being located in a central region located between said first end and said second end, and in that the struts comprise threaded ends, the struts being secured to the metal plate by bolting, characterized in that the walls comprise two metal plates placed end-to-end, said formwork further comprising an assembly rod only deposited on the struts and/or on the bars, said assembly rod (80) comprising a protrusion at each of its ends.
 2. The permanent concrete formwork according to claim 1, wherein the assembly rod is adapted to be placed inside the internal volume of the formwork facing the connection between the two metal plates.
 3. The permanent concrete formwork according to claim 2, wherein the bars located at the periphery of the metal plates have a diameter greater than the diameter of the bars located in the center of said metal plates and/or the number of bars per unit area is greater at the periphery of the metal plates than in the center of said metal plates, the assembly rod resting on the bars at the periphery of the metal plates.
 4. The permanent concrete formwork according to claim 2, wherein the formwork comprises a sealing plate disposed on the formwork outside the internal volume and removably secured to struts, the sealing plate being located at the ends of two metal plates adjacent over an entire height (H) of the two metal plates, so that the sealing plate overlaps said two metal plates adjacent over their entire height (H).
 5. The permanent concrete formwork according to claim 2, wherein said formwork comprises an alignment beam disposed on the formwork outside the internal volume (40) and removably secured to struts, said alignment beam being secured to two metal plates adjacent over at least half a length (L) of the metal plates.
 6. An assembly comprising two permanent concrete formworks according to claim 1, wherein said formworks are assembled so that the assembly is L-shaped and that the internal volumes of said formworks communicate with each other, the assembly (200) further comprising connection rods for securing said formworks together, a first connection rod comprising a first end secured to a wall of a first formwork and a second end comprising a protrusion and located inside the internal volume of a second formwork, a second connection rod comprising a first end secured to a wall of the second formwork and a second end comprising a protrusion and located inside the internal volume of the first formwork.
 7. The assembly comprising two permanent concrete formworks according to claim 1, wherein said formworks are assembled so that the assembly is T-shaped and that the internal volumes of said formworks communicate with each other, a first formwork comprising a first wall that comprises two metal plates located facing a plate metal forming a second wall of said first formwork, a second formwork being located between the two metal plates of the first wall of said first formwork, said assembly further comprising connection rods for securing said formworks together, a first connection rod comprising a first end secured to the metal plate forming the second wall of said first formwork and a second end located inside the internal volume of the second formwork, a second connection rod comprising two ends that comprise each a protrusion and that are located in the internal volume of said first formwork.
 8. The assembly comprising four permanent concrete formworks according to claim 1, wherein said formworks are assembled so that the assembly is cross-shaped and that the internal volumes of said formworks communicate with each other, said assembly further comprising connection rods for securing said formworks together, a first connection rod comprising a first end that comprises a protrusion and that is located in the internal volume of a first formwork, and a second end that comprises a protrusion and that is located in the internal volume of a second formwork, a second connection rod comprising a first end that comprises a protrusion and that is located in the internal volume of a third formwork, and a second end that comprises a protrusion and that is located in the internal volume of a fourth formwork.
 9. A method for manufacturing a metal-concrete composite structure comprising: providing a permanent concrete formwork according to claim 1; casting concrete inside the internal volume of the formwork.
 10. The manufacturing method according to claim 9, further comprising: securing a platen to at least one strut of the formwork by bolting.
 11. A metal-concrete composite structure obtained according to the manufacturing method according to claim
 9. 